1. Technical Field of the Invention
This invention relates to chromium alloy plating containing molybdenum and iodine (hereafter Cr--Mo--I type alloy plating). This chromium alloy plating film is ideal for use on sliding members and corrosion resistant members because of superior heat resistance, wear resistance, corrosion resistance and corrosion-wear resistance properties.
2. Description of the Related Art
Hard chromium plating is used in cylinder liners and piston rings in internal combustion engines. This hard chromium plating film can be used only in a limited atmosphere since the plating softens at hot temperatures in excess of 200.degree. C. causing wear resistance to decrease and the plating itself dissolves due to sulfuric and hydrochloric acid.
Hard chromium plating is regarded as chromium-hydrogen type alloy plating. The hydrogen in the hard chromium plating imparts hardness. However, this hydrogen is discharged at high temperatures bringing about a resultant drop in hardness and wear resistance.
On the other hand, chromium alloy plating containing molybdenum (hereafter Cr--Mo type alloy plating) was proposed to improve the heat resistance, wear resistance and corrosion resistance of the chromium plating film (Japanese Patent Publication No. 44-73574, The Journal of the Surface Finishing Society of Japan (Vol. 21 (1970), No.7, Page 356, or The Journal of the Surface Finishing Society of Japan Vol. 40 (1989), No.3, Page 387).
However, follow-up testing revealed these alloy platings were difficult to reproduce and the electric current efficiency was below 3 percent (plating speed less than 4 .mu.m/Hr) and could not be manufactured economically.